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First, you must determine if you really need to replace a thermostat. Many thnermostats are replaced by someone who want to controll a overheating problem. Doing that will seldom, if ever, will solve a overheating problem. A thermostat will only control what temperature the engine reaches before coolant will flow through the engine.A 190 degree thermostat is normal for modern engines.

To remove a thermostat for whatever reason require the following steps: 1.) Remove two bolts from the thermostat housing located at the end of the return hose (top hose) on the radiator. 2.) Pry out the old thermostat with a screwdriver. 3.), Scrape the thermostat locating lip clean on the manifold.4.) Install the new thermostat in place of the old one.5.) Apply some Locktite High-Tack sealer to the gasket surface of the thermostat housing. 6.) Clean the thermostat mating surface on the intake manifold. 7.) Place the thermostat gasket furnished with the new thermostat to the Loctite High-Tack sealer you applied to the thermostat housing mating surface and align the two holes in the gasket with the holes in the housing. Do not apply sealer to the manifold side of the gasket. Let the gasket set for fifteen minutes for the gasket sealer to cure. Never use silicone type sealers anywhere on an engine. 8.) Install the thermostat housing and gasket over the new thermostat. 9.) Reinstall the two bolts only finger tight to make sure they are not cross-threaded. 10.) Tighten the two bolts with a socket and ratchet wrench alternately and carefully to 24 lb. torque in 8 lb increments. .11.) Start the engine let it warm to the operating temperture of the thermostat and look for leaks around the thermostat housing. Sometimes a minor leak will be seen for a few days until the gasket swells and seals. 12.) If a leak is seen after a few days, tighten the bolts again evenly and carefully up to 1/8 turn or a an additional 2 lb. torque. Overtightening can break the thermostat housing.

It is seldom the thermostat that causes heater problems. If your engine is running at the correct operating temperature, the heater core will also be hot if it is properly connected to the engine with an in and out heater hose.

The problem may be bad heater fan motor and can be tested. If the fan motor is good, it is a kinked or a disconnected vacuum line, a disabled heater control switch or it could be that the linkage that opens the register (heater door) is disconnected. The register is located inside the heater plenum and the vacuum lines and controls are located under the dash If the fan is operable and if the register in the heater plenum does not open, warm air from the heater core cannot enter the pasenger compartment.

If the heater core has recently be replaced, the person who did that work accidentally disabled the register controls.

ok. The heater core hasn't been replaced. Only work that was done on it recently is that we had the fuel pump replaced. Just bought the blazer 2 months ago. When we test drove it we tried the heater and it blew out nice hot air. Now, it is not and it is getting very cold here. I don't know what to try first and I don't want to have to take it to a shop. Thanks for any help!

Whenb the engine is warm, does the heater blow cold air? If it does, the heater fan os OK. After the engine warms up to operating temperature, turn on the heater and feel around on the heater plenum under the dash and see if it is warm. If it is warm, the hot air from the fan through the heater core is being blocked by a closed register. You must find out why the register is not opening. Eith vacuum line is disconnected or the switch to the register linkage is binding.

The plenum is the plastic air box that is under the dash that has heater outlet vents and is attched to the heater fan and core assembly that is located on the engine side of the firewall.It contains directional doors that are controlled by the vacuum diaphrgams and those are contriolled by the heater contol switch.

If the engine is operating normally, but there is no heat in the core, it is very possible that the core is plugged up. These vehicles do not use a heater control valve, they always run the water through the core and use a baffle to bring warm air into the vent system. Check to see if the feed and return lines to the heater core are both hot. If one is noticably cooler than the other, the core needs to be flushed. If it is plugged, probably a good idea to replace the Dexcool. Use Dexcool again, don't mix with the green stuff!

If both feed and return are hot, you have a baffle not operating in the duct work. Haven't worked on these before, but there are others on the maintenance and repair board that have.

It is best to get the reasonably priced Prestone Radiator flush kit and use Prestone radiator flush solution. The kit has a radiator cap adapter and a permanent water hose T-fitting that is placed in the heater hose. You can start the motor and let the engine's water pump flush the system using a garden hose to drain the solution away from the vehicle into a container. Do not disturb the radiator drain cock. It is plastic and may be damaged if you try to open it and besides, it is troublesome to get to. Just in case you damage the drain cock, a replacement is offered by Dorman, part no. 61109. They are short stem, push in with captive thread. There is no need to replace the thermostat unless it needs to be replaced for some reason. If your heater is not blowing warm or hot air, it is seldom the fault of the thermostat. Thermostats are unnecessarily replaced far too often in a futile attempt to solve a engine cooling or a heater problem. Feel each heater hose after the nengine is warmed to operating temperature and if one hose is cold to the touch, your heater core is stopped up and needs to be replaced..

My Blazers engine light has been coming on lately once it gets to around normal operating temp ,it blows good warm air but seems to be just below its usual operating temp.After a harsh cold snap it would not start. once i got it going it seemed to run a little rough once it warmed up.I am thinking it would not hurt to change the thermostat.I warmed it up today and then I checked the hoses after and found that the top hose was warm and the bottom hose was cold and the thermostat housing was leaking.The only thing I am not really sure of is where the drain plug is on the rad and how does it open.I think I found it on the passenger side but I am not sure.Does any of this make any sense?I am more familiar with older vehicles so this is fairly new to me.

I just changed the thermostat on my '02 a couple of days ago. I ended up pulling the top hose at the radiator and aiming it down to a bucket under the car. you will probably have to pull the cruise and throttle cables and their brackets from the throttle body to get to the back thermostat bolt. I know it looks like nuts on studs, but it is a bolt with a stud on top.

Once you get the hose off and the coolant down, the whole job takes about ten minutes.

And yep, if the thermostat is not closing fully, the engine will not warm up in the prescribed time and the light will come on with a P0128 code set.

I have recently ran into a temperature problems with my 2000 Blazer. I recently replaced the heater core in May of 08. So I don&#146;t think that is the problem. My Blazer still blows warm but not hot air, and the defrost works but not the best. My temperature gage flocculates from normal of just under 210 to almost over heating, but as soon as it gets close to that point it shoots back to the cooler side (This happens when driving). The Blazer is going through a gallon of Antifreeze every two too two and half weeks. I have not noticed any leaks coming from the engine.

Any suggestions on what it could be would be helpful.

I am mechanically challenged, and am not to sure what the problem could be. I would like to solve it before it grows to a bigger more expensive ordeal.

If you are going through that much antifreeze and don't have an external leak, you are running it out the tailpipe or filling the crankcase. Have you checked to see if the overflow tank is cracked? Seriously, that is a lot of fluid loss to not be showing up somewhere. Any smoke out the tailpipe when you first start up?

I hate to be the bearer of bad news, but if you are going through that much antifreeze and not finding a leak, it is going to be expensive. If it is not leaking, it is probably being burned in the engine. That could mean intake manifold gasket, head gasket, that sort of thing. Not a job you would want to tackle yourself as it is a big job even for an experienced do it yourselfer.

I yesterday I put in more antifreeze, and then discorved a leak. I took it to Autozone to get a read on my check engine light to see if that was part of the ordeal. After the scan two codes came up, P0101 and P0420. The print out that was given to me listed several things for each number.When I asked the guy to give more details on the items that it had said, it did not seem like he knew what he was talking about. Here is some of the things that were listed,P0101:1.Vacuum hose off2.Throttle body intake tube loose, cracked or off3.BARO (Barometer)/ MAP Manifold Absolute Pressure defective4.VAF (Vane Air Flow) MAF (Mass Air Flow) sensor dirty or defective.

The guy at Autozone said I should try and do the vacuum leak first cause it showed up on both of them. Now, to me,he did not know what he was talking about, so i want to make sure before undertaking this ordeal it is handled the right way the first time.

If any of those could be linked to the leakeage of antifreeze and the heat not working, could you let me know. : ) Thanks car guys.

Where did you find the antifreeze leak? If you found it up on the intake manifold area, you probably have a blown intake gasket which would cause all sorts of problems such as what the code reader found.

Intake manifold gasket failure is somewhat common on high mileage 4.3L engines.